The invention generally relates to systems and methods for determining or estimating the distance between objects, and relates in particular to systems and methods for estimating the distance between objects that include digital electronics.
Many systems and methods have been developed for estimating the distance between electronic devices. For example, a received-signal-strength-indication (RSSI) method of estimating the distance between two communicating analog electronic devices employs measuring the strength of the received signals. The power of a radio signal for example, falls off exponentially with distance, and the receiver can measure this attenuation in order to estimate the distance to the sender. This cannot be applied directly to digital devices however, without significant change to the hardware, in part, because noise and interference easily affect the measured results.
Another method for estimating the distance between devices includes using sonic transceivers, but the use of sonic transceivers also increases hardware costs as well as power consumption. Global position systems (GPS) may also be used to determine distance, but such systems also increase hardware cost.
A further type of distance determining system relies on a pre-deployed sensor network. The distance between the device and pre-deployed sensors are estimated first, and the sensor network calculates the location of the device. Again, such a system increases hardware cost.
Conventional systems for estimating the distance between two wireless communication devices include time-of-arrival (ToA) and angle-of-arrival (AoA). The ToA method is based on the speed of radio wave propagation and the measured time it takes for a radio signal to move between two objects. Combining this information allows the ToA system to estimate the distance between sender and receiver. ToA offers high levels of accuracy, but also requires relatively fast processing capabilities to resolve timing differences for fine measurements. This problem is amplified over short distances, making ToA a poor choice for a ranging technique for positioning in wireless, ad-hoc sensing networks. ToA measurements may be combined with acoustic measurements to achieve accuracy of a few percent of the transmission range. Acoustic signals, however, are temperature dependent, require unobstructed line-of-sight, are reliant on directionality, and require additional hardware.
The AoA techniques make use of antenna arrays to measure the angle at which a signal arrives. Angles can be combined with distance estimates or other angle measurements to derive positions, but this requires multiple antennas that may be located far apart, which also increases hardware cost of the devices. A major disadvantage of the AoA techniques is the hardware requirement. The antenna arrays are expensive to be implemented and maintained, making AoA a poor choice for inexpensive applications.
There remains a need, therefore, for an efficient and cost effective system and method for providing accurate estimated distances between wireless digital electronic devices.